Until recently, mobile wireless equipment used separate Integrated Circuits (ICs) for the Radio Frequency (RF) transceiver, the baseband (BB) processor and the Power Management Unit (PMU). In the context of the permanent perpetual quest for cost reduction, the approach taken by most IC vendors is that of a single chip, made up of either a single RF CMOS die, or multiple separate dies, which integrates into a single package all three previously listed ICs, namely, RF, BB and PMU into a single package.
FIG. 1 illustrates the general architecture of a multiple-band 2G/3G phone 100 consisting of a quad band 2.75G (EGPRS), triple band 3G (HSPA+) with 3G receive diversity.
There is illustrated the concept of a RF-BB-PMU Integrated circuit die 190 particularly advantageous because of the cost saving in the manufacturing process. Indeed, thanks to the use of such a single die 190, the whole telecom pipe of the mobile phone now only requires very few extra additional components to make a phone call: one or several Power Amplifier(s) (PA) and its associated front-end circuitry such as RF bandpass filters, duplexers, antenna switch etc.
More precisely, FIG. 1 shows the following components which are typical of a modern mobile:
    Label 110: General architecture of the mobile phone's RF front-end.    Label 111: Antenna switch. Allows switching from one frequency band to another.    Label 112: 3G (HSPA) duplexer. Connects TX and RX path to the antenna switch.
Provides RF isolation between RF tx and RF rx chains,    Label 113: 2.75 G (EGPRS) power amplifiers    Label 114: 3G (HSPA) power amplifiers    Label 115: Diversity receiver RF bandpass filters    Label 190: Single die/single-chip RF (label 120)-BB(label 130)-PMU (label 140) IC.    Label 120: Multi-standard, multi-band RF transmit/receive (transceiver) IC.    Label 130: Digital baseband (DBB) IC
There is thus shown one illustrative example of the integration, within one single die 190, of a RF Front End circuit 110, a 2G/3G RF transceiver 120, a baseband 130, a PMU unit 140 and possibly DDR memory 150, being either external or internal.
RF Front-End circuit 110 supports quad band 2G (Band II, III, V, VIII EGPRS), triple band 3G (WCDMA I, II, III) which is typical of recent mobile phone architecture, the selection of the particular mode/band being performed by means of an antenna switch 111 which directs the signal to the appropriate set of front end filters 112. Conversely, antenna switch 101 directs the transmit signal generated by the appropriate 2G or 3G Power amplifiers, respectively 113 and 114, to the antenna.
2/3G transceiver 120 includes the conventional circuits required for achieving a 2G or 3G mobile communication, such as, in the receiving chain, Low Noise amplifiers (LNA) 121, a Rx VCO Frequency synthesizer 122 with appropriate division circuits (represented by local divider LO Div), a circuit 123 achieving programmable Gain amplifier (PGA), Analog to digital converter (ADC) as well as DSP processing. On the transmitting chain, transceiver 120 includes a circuit 126 achieving PGA, Digital to Analog (DAC) conversion as well as DSP processing, a Tx VCO frequency synthesizer 125 associated with dividing circuits (LO Div), and conventional digitally controlled Gain amplifier 124. Transceiver 120 further includes appropriate timing circuits 126 as well as a RF-BB baseband interface 127 for interfacing the baseband 130. For the sake of clarity, the different control, data and clock signals which are represented in FIG. 1 (such as RFBBi_EN, RX data 1, RX data 2, TX data 1, SYSCLKEN, SYSCLK) are conventional and known to the skilled man and do not need any further discussion.
Similarly, baseband 130 achieves communication between the transceiver 120 (through interface 127) with different devices and peripherals, such as two cameras 160, two displays 170, a USB device 180 through appropriate data and control leads (including CLK clocks and Chip Select CSi) as well as external DDR memory.
It can be seen that the integration of those components in a single die clearly reduces the cost of manufacturing a handset since the telecom pipe of the mobile phone now only requires very few extra additional components to make a phone call: one or several Power Amplifier(s) (PA) and its associated front-end circuitry such as RF bandpass filters, duplexers, antenna switch etc.
While the single chip RF, BB, PMU presents a significant cost reduction of the entire mobile phone chipset, there are significant EMI problems to be considered.
Indeed, it has been noticed that with such an architecture, the RF transmit modulator chain is victim of a digital aggressor activity creating clock and/or data activity related frequency spurs.
Such aggressor might be, for instance and without any limitation, the camera interface(s) digital bit stream and associated clock, the display interface(s) digital bit stream and associated clock, the USB port, the external memory data and clock bus, Power management Unit (PMU) internal clocks, digital Baseband clock spurs etc. . . .
For the sake of clarity, the following “aggressors” are highlighted in FIG. 1: the DDR memory 150, the cameras 160, the display 170, the USB interface 180 etc. . . . which pollute the “victim” being the RF block of 2G/3G RF transceiver 120.
The pollution of the transmitter block of the RF chain results in modulation of the noise generated by EMI contributors through the uplink transmission carrier, thus causing pollution to the RF receiver of the same mobile phone or even the RF receivers of the other mobiles located in a close vicinity.
In order to minimize the effects of pollution generated by the different “aggressors” some techniques have already been used.
One conventional solution which is known in the art consists in clearly isolating, on a time division basis, the operating of both RF transmitter and the digital base band. This know solution is designated under the general reference of Time Division Isolation (TDI) . . . . And can be used in the context of the GSM with bursts accesses to the RF transmission. Therefore, one can avoid, by means of such TDI technique, the simultaneous use of the victim with the aggressor(s).
The TDI can clearly be used in the case of GSM showing bursted access to the RF transceiver . . . however, 3 G communications are full duplex and further requires continuous use of both the RF transmitter and the RF receiver, thus preventing any possibility of TDI.
Furthermore, it has been noticed that the so-called TDI technique also results in some waste of the digital processing resources offered by the baseband which remains idle during the activation of the RF transmitter (for instance).
Such waste of resources is simply not acceptable in the perspective of the design of new mobile phones which incorporate highly sophisticated multimedia functionalities requiring a great number of processing resources.
At last, the TDI technique does not prevent the emitter of one mobile, for instance a first mobile emitting in the uplink to its base station, to spoil the receiver of a second mobile located in the neighborhood of said first mobile, when the second is receiving in downlink from its own base station.
Other techniques are known for improving the isolation of the RF receiver which are known in the art. Such techniques are based on the use of specific layout arrangements of the microelectronics circuits (Deep Nwell, stop layers), special shielding circuits or frequency uses for the purpose of reducing, as much as possible the effect of the transmission to the receiver located in a neighboring mobile.
It is highly desirable to improve additional technique which still improves the protection of the RF transmission of mobile phones.